Materials of the earth’s crust Social Materials of the earth’s crust

Rocks and Minerals: The lithosphere is made up of rocks and minerals. Rocks are those materials which are obtained from the earth’s crust. They include not only the hard materials such as granite and marble, but also soft and loose materials such as chalk, clay, sand and salt. Rocks are made up of minerals. They do not possess a definite chemical composition. Minerals are naturally occurring substances present in rocks. These are solid substances which have a definite chemical composition.

Types of rocks: Different types of rocks are formed in different ways. Thus, they have different characteristics with regard to their composition, colour, size and texture. On the basis of their mode of formation, there are three major types of rocks-igneous, sedimentary and metamorphic.

Igneous rocks: Igneous rocks (from the Greek word for fire) form from when hot, molten rock crystallizes and solidifies. The melt originates deep within the Earth near active plate boundaries or hot spots, then rises toward the surface. Igneous rocks are divided into two groups, intrusive or extrusive, depending upon where the molten rock solidifies.

Sedimentary rocks: Sedimentary rocks are formed from pre-existing rocks or pieces of once-living organisms. They form from deposits that accumulate on the Earth's surface. Sedimentary rocks often have distinctive layering or bedding. Many of the picturesque views of the desert southwest show mesas and arches made of layered sedimentary rock.

Metamorphic rocks:  Metamorphic rocks form when rocks are subjected to high heat, high pressure, hot mineral-rich fluids or, more commonly, some combination of these factors. Conditions like these are found deep within the Earth or where tectonic plates meet.

By, M.Kanishka 7 ‘A’ Thank You